A method and a device according to the present invention are used to attach electrical components to circuit boards.
A mounting bracket for electrical components is already known from the related art.
The mounting bracket is formed as a flat U-shaped structural element, a circular shaped area being a located between its legs which extend vertically downwards. The two vertically extending legs terminate in soldering pins on which shouldered bearing areas are formed. The U-shaped mounting bracket is supported with these shouldered bearing areas on the circuit board after being pressed into it. In this manner, the component mounted in the circular area is always held at a constant distance from the surface of the circuit board.
The U-shaped structural element is pressed into the circuit board with its soldering pins; however, with such an attachment it is difficult to support large and heavy electrical components only at the bottom of the circuit board in a shock-resistant manner. Use of a large number of U-shaped structural elements for the mounting of large and heavy components significantly limits the installation space available on the circuit board for other components.
In addition to the outlined inadequacies of the devices known from the related art, the requirements on safety-relevant switching devices for use in automobiles have also increased sharply in relation to mass and constructional design. The mass and constructional design of electrical components are limited by strain on the soldering points, which often makes the use of standard parts difficult and requires more expensive electrical components. Furthermore, in airbag applications, for example, the acceleration sensors are mounted on a separate circuit board in order to prevent the airbags from being inadvertently triggered by intrinsic movements caused by resonant step-ups. These intrinsic movements cannot be eliminated completely when circuit boards are assembled with known assembly methods, for which reason the acceleration sensors for airbags have been mounted on an additional circuit board separated from the circuit board already mentioned.
The attachment method according to the present invention makes it possible to achieve a smaller and more compact construction for switching devices since the connection of the electrical components with the housing enclosing them creates an additional point for the absorption of thermal and mechanical stresses in addition to the connection with the circuit board. As a result, not only the soldering point now absorbs the occurring stresses but rather both of the created connection points, which eliminates the size limitation of the electrical components resulting from the strain on the soldering point. Since the additional connection of the components with the housing relieves the stress on the connection of the electrical components with the circuit board, the circuit board can be made less solid, resulting in space being made available for the integration of additional circuit parts. This permits the elimination of an additional circuit board and results in significantly more compact and smaller-sized switching devices.
In additional embodiments of the attachment method according to the present invention, the requirements of a production line for mass production of switching devices can be met by having the electrical components positioned in a defined position relative to the circuit board by the use of retaining devices. These can absorb the thermal and mechanical stresses during the production process, resulting in a reduction of stress on the soldering points, in particular. The additional connection beyond the connection with the circuit board is made by cementing the electrical component to the housing enclosing it. Advantageously, the electrical component can be connected to the top of the housing, resulting in two opposite connection points, namely with the circuit board and with the top of the housing. In addition to the top of the housing, the electrical component may also be cemented to an adjoining housing wall. In order to produce the adhesive joint, a bead of adhesive preferably of silicone adhesive is introduced between the housing and the surface of the electrical component to be affixed.
In addition to an attachment method, the present invention relates to a switching device having electrical components which are both secured to the circuit board and connected to the housing, the housing having a structure adapted to the electrical component. In an advantageous embodiment of the housing structure, it is designed as ribbed structure; the ribbed structure can be provided both on a housing top covering the electrical component and on a wall of the housing adjoining the electrical component. The ribbed structure includes ribs that are sized differently in height and width between which pockets for receiving excess adhesive are positioned. In order to improve the positive fit of the adhesive bead and the surface of the electrical component to be affixed, recesses or projections may be provided on the surface of the electrical component, making it possible to eliminate a relative motion between the component and the housing at the adhesive joint. Moreover, the ribbed structure on adjoining housing parts serves to increase the effective adhesive joint surface between the adhesive bead and the housing.